Adding a single char to a char pointer.

Applications Programming
1

Hello,

I'm trying to write a method which will return the extension of a file given the file's name, e.g. test.txt should return txt. I'm using C so am limited to char pointers and arrays. Here is the code as I have it:

char* getext(char *file)
{
        char *extension;
        int i, j;

        for(i=strlen(file); i>0; i--)
        {
          if(file == '.') {
                for(j=i; j<strlen(file); j++) {
                        strcat(extension, (const char *) file[j]);
                }
                return extension;
          }
        }
        return extension;
}

I know this could return a null pointer but I'm just trying to get it working before I clean it up. I'm getting this compile warning:

utils.c:106: warning: cast to pointer from integer of different size

Line 106 is the strcat() call. Does somebody have a simple way of adding a single character to a char pointer? I'm not a great C programmer and have never really fully understood the concept of pointers.

Thanks for your help.

2

I think your making this harder then it needs to be. Check out the index/rindex() functions.

char* getext(char *file)
{
   char *extension = NULL;

   extension = rindex(file,'.');
   // check for NULL here

   // use this to remove the dot
   return ++extension;
}
3

Or something like:

char* getext(char *file)
{
  int i;

  for(i=strlen(file)-1; i>0; i--)
  {
    if(file == '.') {
        return file+i+1;
    }
  }
  return NULL;
}

Regards

4

Make sure your files only have one extension with either of these solutions in the event you have files named like

myFile.tar.gz

5

my solution would work as it reads from the right.

myFile.tar.gz would return gz

6

Thanks to everybody for your help. I ended up going with frank_rizzo's suggestion and I now have it working. I didn't even know about the rindex() function so that would probably be why I was trying to make it harder for myself than it had to be.